Cracks that form within materials can be difficult to detect and almost impossible to repair. A successful method of autonomically repairing cracks that has the potential for significantly increasing the longevity of materials has been described, for example, in U.S. Pat. No. 6,518,330. This self-healing system includes a material containing, for example, solid particles of Grubbs catalyst and capsules containing liquid dicyclopentadiene (DCPD) embedded in an epoxy matrix. When a crack propagates through the material, it ruptures the microcapsules and releases DCPD into the crack plane. The DCPD then contacts the Grubbs catalyst, undergoes Ring Opening Metathesis Polymerization (ROMP), and cures to provide structural continuity where the crack had been.
Materials used in medical implants could benefit from having autonomic self-healing properties. Failure of these materials can be harmful or even fatal to the patient, and may require surgical intervention to repair the damage or to replace the material. In one example, fatigue and/or failure of bone cements used in artificial hip or knee implants can result in the formation of debris particles. These particles can contribute to aseptic loosening, in which inflammation of the natural tissue leads to bone destruction and loosening of the prosthesis. In 2004, revision surgeries performed in the U.S. to repair or replace hip or knee implants cost over $3 billion in hospitalization fees.
Bone cement based on poly(methyl methacrylate) (PMMA) has emerged as one of the premier synthetic biomaterials in contemporary orthopedics, and is used for anchoring prostheses to the contiguous bone in cemented arthroplasties. The bone cement formulation typically includes a liquid component and a solid component. The liquid component includes methyl methacrylate (MMA) monomer, and typically includes a tertiary aromatic amine accelerant such as dimethylamino-p-toluidine (DMPT) or dimethylaniline (DMA). The solid component includes a polymerization initiator such as benzoyl peroxide (BPO), a combination of PMMA and poly(styrene-co-methyl methacrylate) beads, and a radiopacifier such as barium sulfate. The liquid and solid components are mixed together just before use to form a grouting material that quickly sets due to polymerization of the MMA monomer.
Bone cement has a number of disadvantages. Toxicity of some of the reactants can lead to chemical necrosis. The high exotherm of the polymerization of MMA to PMMA can lead to thermal necrosis. Weak link zones can be formed, particularly at the bone-cement interface and at the cement-prosthesis interface. These disadvantages can contribute to aseptic loosening and/or other complications during and/or after surgery, and often lead to revision surgery.
Attempts at developing a self-healing bone cement have included using a polyester matrix material; a monomer mixture containing 35 weight percent (wt %) styrene, 35 wt % divinyl benzene and polystyrene (35 wt %); an accelerant containing cobalt (II) naphthenate and DMA; and methyl ethyl ketone peroxide (MEKP) as an initiator for the polymerization of the monomer mixture (Hegeman, A. J. Self Repairing Polymers: Repair Mechanisms and Micromechanical Modeling; Master of Science thesis; University of Illinois at Urbana-Champaign: Urbana, Ill., 1997). These attempts have met with mixed success, and likely have suffered from an insufficient amount of initiator in the crack plane of the damaged bone cement.
It is desirable to provide a self-healing bone cement material. It is also desirable to provide a self-healing material in which the healing is more rapid and/or robust than in conventional self-healing materials.